Method of cleaning and preparing metal for paint



Patented May 7,1940

, PATENT OFFICE METHOD OF CLEANING AND PREPARING METAL FOB PAINT Howard B. Neilson, Detroit, Mich.

No Drawing. Application June 8, 1938, Serial No. 212.542

'2 Claims.

This invention relates to improved composition and method for cleaning and treating metal preparatory to coating with a finishing material such as paint, lacquer, enamel, or similar finishing materials, generally termed paint. This application in certain respects relates to improvements in the compositions and methods disclosed in U. S. Patent No. 1,935,911, issued to me on November 21, 1933, and in certain respects is a continuation-ln-part of my co-pending application, Serial No. 49,035, filed November 9, 1935, issued July 18, 1939, as Patent No. 2,166,476.

Heretofore, metal cleaning compositions of the acid type have included a rust dissolving and metal etching acid such as orthophosphoric acid, water, an oil and grease solvent, a surface tension reducing and spreading agent, and a body building constituent for causing the material to cling, temporarily at least, to other than horizontally disposed surfaces. Phosphoric acid dissolves oxides, rust and rust formations, and corrosion promoting salts and agents, etches the metal to produce the desired roughness or tooth on the surface of the metal so that the paint may be firmly bonded to the surface thereof, and to some extent causes the formation of a phosphate deposit on the metal which prevents rusting or corrosion beneath the paint and increases the strength of the bond between the metal and the finishing materials. However, to enable the phosphoric acid to effect the above purposes, it must contact or reach the metal surface promptly upon application of the cleaning material. Oil and grease solvents, especially ether derivatives of ethylene glycol, ketones, alcohols, and similar organic solvents which are miscible in both water and oil, have been employed to break up and disperse oil and grease films and formations to enable the phosphoric acid to contact the metal and do its work. Such organic solvents, however, in the presence of phosphoric acid, cause the cleaning composition to have high surface tension characteristics which in turn cause the cleaning liquid to collect on the metal surface in globules, or stringy vein-like streaks, rather than spread over all parts of the metal surface. This results in stained or unevenly cleaned metal surfaces.

As disclosed in the Neison Patent No. 1,935,911, issued November 21, 1933, surface tension reducing and spreading agents have been employed to overcome this difficulty and secure even spreading of the cleaning solution and uniform cleaning of all parts of the metal surface. The most effective organic solvents heretofore employed which are miscible in both water and oil are relatively expensive materials and constitute a considerable portion of the cleaning composition.

The principal object of this invention is to improve the art of cleaning and treating metals preparatory to painting.

Another object is to efiect a reduction in and in some instances entirely'eliminate the expensive oil-miscible and water-miscible solvents employed in a cleaning composition.

Another object is to provide surface tension reducing, wetting and spreading agents which also effect, in part at least, the functions ordinarily accomplished by the oil and grease solvent constituent of an acid-type metal cleaning composition.

A further object is to provide in a cleaning composition, surface tension reducing, wetting and spreading agents which increase the effectiveness of any oil and grease solvent which may be employed in an acid cleaning composition.

Another object is to provide in an acid-type of metal cleaning composition which includes surface tension reducing, wetting and spreading agents, cheap solvents which have heretofore been comparatively ineffective when it has been attempted to dissolve and disperse oil and grease by their use. p

A further object of the invention is to provide an acid-type metal cleaning composition which enables the acid constituents thereof to become substantially completely effective by reducing to a minimum constituents which would inhibit or impede the action of the acid in etching metal.

Another object is to provide an acid type of metal cleaning composition which permits the acid constituent to completely expend itself even though the composition is allowed to dry on the metal.

A further object is to permit the use of relatively large amounts of acid in an acid-type metal cleaning composition which is to be wiped off from the metal with cloth or other absorbent material.

Still another object is to provide an acid-type of metal cleaning material which requires no removal from the metal either by wiping or washing but permits the acid constituent completely to expend itself and to produce a phosphate deposit which prevents corrosion beneath paint and enhances the strength of the bond between the paint and the metal.

Another object of the invention is to provide surface tension reducing, wetting and spreading agents in an acid-type of metal cleaning com- Working solution Percscnt Peggmt 1 to 1 w we or. per- "F volume cent by volume 75% phosphoric acid 69. 5 57. 2 i9. 07 Glycol butyl ether 17. 25. 0 8.3 Oleic acid 00. t 00. 7 0. 23 Sapomm... 1. 0 0i. 2 0. 4 Water 12.0v 15.9 72.00

Various attempts have been made to reduce the amount of oil and grease solvent in the working solution such as specified in the third column of the above table. For example, the glycol butyl ether content has been cut in half but the resulting composition would not maintain a uniform film on greasy or oily metal, the composition breaking its film and drawing together so that parts of the surface of the metal were not contacted by the cleaning material. Increasing the amount of saponin or oleic or both does not remedy the defect. I have found, however, that if to such a composition, with the reduced amount of oil and grease solvent, less than onetenth of one percent of a sodium salt of an acid sulphate of multiple carbon, saturated, branched chain, secondary alcohol having the general formula:

R H-OSOaNa in which R and R." represent aliphatic hydrocarbon radicals, R plus R containing a total number of carbon atoms ranging from six to seventeen, the cleaning composition maintains a uniform film and that the cleaning composition is very efiective even though the metal is covered with grease or oil. The above mentioned sodium salts of the acid sulphates of multiple carbon, saturated, branched chain, secondary alcohols having the above mentioned general formula are usually referred to simply as sodium secondary alcohol sulphates. From one-eighth to two percent of a 25% water solution, by weight (25% of secondary alcohol sulphates dissolved in 75% of Water), of the above mentioned sodium secondary alcohol sulphates have been found satisfactory in the working solution of the cleaning material.

It is desirable to reduce the amount of oil and grease solvent such as glycol butyl ether to a minimum or even to omit it if possible and also to reduce to a minimum the amount of wetting and spreading agents employed both because of the fact that these are among the more expensive materials employed in an acid-type metal cleaning composition and also because of the fact that a reduction in the amount of organic compounds employed in such a cleaner reduces the phoric acid in etching the metal surface. I have also discovered that the use of approximately 1%, by volume, of the water solution of the sodium secondary alcohol sulphates (25% water solution, by weight) permits the omission of both the saponin and oleic acids and still provides a very workable cleaning material. The omission of only the oleic acid increases the spreading effect of the cleaning material which is desirable since it permits the cleaner to act in seams, crevices, and at similar inaccessible points of a metal article to be cleaned. It is noted that where the cleaning material is to be removed by wiping of the same with cloth or absorbent material, it is at times desirable to retain a slight percentage of saponin since this in certain instances expedites the wipe-up step.

I have discovered that a water solution of an acid cleaner in dilute form, used as the working solution, may include simply: phosphoric acid 75% by weight; from 5 to by volume; from one-eighth of 1% to 2% of a 25% water solution of a sodium secondary alcohol sulphate and the balance, approximately 89% to 94% Water. This material forms a workable composition for etching metals, removing rust, oxides and other foreign matter, dissolving grease and oil and dispersing the same throughout the 'cleaning solution. It has heretofore been believed necessary to provide a grease solvent constituent in addition to a wetting agent in an acid type metal cleaning composition. The specified composition is preferably appliedto the metal to be cleaned by a spraying process in order to produce a certain amount of agitation or by scrubbing with a brush as the material is applied to the article to be cleaned. It is noted that if larger amounts, from about 2 to 4% of the 25% water solution of the sodium secondary alcohol sulphates are employed, there will be an increase in the amount of the phosphate deposited on the metal. The above described composition, in condition to use, contains approximately 90% by volume, of water. If the cleaner is to be shipped or transported considerable distances to the point of use, it is desirable to supply a concentrated material by eliminating a large part of the water therefrom and then diluting the material at the point of use. This eliminates transportation charges upon Water which constitutes a large part of the weight and bulk of the above described material. It is noted, however, that in concentrating the material, over 16% phosphoric acid has a tendency to throw out the sodium secondary alcohol sulphates from a water solution unless some blending agent is employed. If 5 to approximately, of the concentrated material is made up of organic solvents including ketones, such as dimethyl ketone (acetone), or ethyl methyl ketone (butanone), isopropyl alcohol, monobutyl or monethyl ethers of diethylene glycol, or mono-ether derivatives of ethylene glycol, then the sodium secondary alcohol sulphates will be kept in solution. It is noted that when ethyl methyl ketone is employed, one of the other solvents mentioned should form a part of the blending agent since the ethyl methyl ketone itself is not wholly miscible with water. With the exception of the ether derivatives of ethylene glycol, such as the monomethyl, monoethyl, and monobutyl ethers of ethylene glycol, all of the above mentioned solvents are usually considered to be but partially or non-effective as oil and inhibiting efiect upon the action 01 the phosgrease solvents. A composition of this character may consist of, by volume:

Per cent Phosphoric acid 20 to 40 Sodium secondary alcohol sulphates (25% water solution, by weight)--- 0.5 to 0.8 Acetone 20 Water Balance This material constitutes a concentrated material which may be diluted with three parts of water to one part of the concentrated material,

by volume, at the point of use. This material is enerally employed as a wipe-off material, i. e., wiped from the article to be cleaned by means of cloths, cotton waste or similar absorbent material. The diluted working solution is essentially the same as that employed with a spray apparatus or some means of agitating the solution during use, such as agitating or scrubbing with a brush, except that the working solution contains approximately 5% of acetone. This acetone content reduces the amount of agitation necessary during use and makes the material somewhat more effective in removing heavy coats of oil or grease. In this working solution there is less than 6% of organic materials and both the acetone and the sodium secondary alcohol sulphates have little or no inhibiting or retarding effect on the action of the acid in etching the metal.

If a wipe-up material is to be diluted to a greater extent at the point of use, it is desirable to employ a composition of the following constitution by volume:

Percentage by volume Phosphoric acid 33 to Monobutyl ethylene glycol 22 Monoethyl ether of ethylene glycol 5 Sodium secondary alcohol sulphates (25% water solution, by weight) 1.5 Water Balance alcohol, or ether derivatives of diethylene glycol Percentage by volume Acetone 10 to 20 Phosphoric acid 68 Molasses 7 7 Sodium secondary alcohol sulphates (25% water solution, by weight) 1.5 Water Balance This wash-off material is diluted at the point of use by three parts of water, by volume, to one of the concentrated material. In this wash-off material, other solvents and blending agents previously mentioned may be substituted for all or part of the acetone content of the above example.

Although several specific embodiments of the invention have been set forth above, it is understood that various changes in the proportions of the ingredients and in the ingredients themselves may be made without departing from the spirit and scope of the invention as defined by the appended claims,

What is claimed is:

1. A metal cleaning composition including principally water and a metal etching acid and comparatively small quantities of a sodium secondary alcohol sulphate and acetone.

2. The working solution of a metal cleaning composition including, water, a metal etching acid, acetone and a sodium secondary alcohol sulphate, the acetone and sodium secondary alcohol sulphate together constituting less than 6%, by volume. of said solution.

HOWARD R. NEIL-SON. 

